532 



NA TURE 



[September 19, 1907 



resolved into two components ; — (i) a vibratory motion of 

 flexion of the body mainly for progression ; (2) a spiral 

 motion of the body as a whole due to the undulating 

 membrane — a spirally wound lateral extension of the ecto- 

 plastic periplast bearing striations (the contractile 

 myonemes). The body of a Spirillum bears flagella, and 

 is more rigid than thai: of a Spirochsele in motion. The 

 so-called flagellate (ciliate) stages of Spirochaetes are 

 merely due to the splitting off of myoneme fibrils from the 

 undulating membrane during its rupture, resulting from 

 violent contortions or approaching death. 



Sonic Points in the Structure oj the Larva of 

 Lanice conchilega. 



The Rev. G. .'\. Elrington described, in the pelagic larva 

 of Lanice conchilega, a gland situated on the dorsal side 

 of the oesophagus, and composed of a cluster of large pear- 

 shaped cells, the thin ends of which converge to the orifice 

 of the giand, which lies in the mid-dorsal line of the" neck" 

 region. I-Vom its staining reactions it is evident that the 

 gland is concerned in secreting the mucin of the gela- 

 tinous tube in which the larva is found enclosed. The 

 gland, which is not present in the adult or in a young 

 worm which was just beginning to form its sandy tube, 

 is evidently a transitory structure, which persists only so 

 long as the larva retains its transparent tube. In the 

 pelagic larva there are three separate nephridia, there 

 being no trace of the fusion characteristic of the nephridial 

 apparatus of the adult. 



Mr. Arnold T. Watson expressed the opinion that the 

 gelatinous tube, in which the larva floats, not only serves 

 as a protection, but is also the means of collecting food 

 particles, which on being brought into contact with the 

 outside of the tube adhere to it. In order to secure this 

 food the larva from time to time partially emerges from 

 one end of the tube and applies to its surface the 

 ciliated groove which runs from end to end of its growing 

 tentacles. Development of the organism is thus carried 

 on to a stage further than would have been possible in 

 the absence of solid food. By the time the animal settles 

 down on the sea-bottom and begins to construct the mem- 

 branous sand-covered tube inhabited by the adult, the 

 mucus-secreting gland, being no longer required, dis- 

 appears, and owing to its dorsal position does so without 

 disturbing the formation of the permanent ventral 

 glandular structures which produce the membranous basis 

 of the tube of the adult. 



The Development of Ophiothrix fragilis. 

 Prof. E. \V. MacBride, F.R.S., described the early 

 stages of development of this common British Ophiurid. 

 Two sets of cultures were studied, the first obtained by 

 fertilising the eggs artificially, the second by allowing 

 the ripe male and female naturally to shed their repro- 

 ductive products. In the first series, segmentation re- 

 sulted in the formation of a morula, an invagination 

 followed, and it then transpired that the interior cells 

 were precociously formed mesenchyme. The ccelom 

 appeared as a single vesicle at the apex of the gut. In 

 the second series segmentation resulted in the formation 

 of a thick-walled blastula, followed by a regular invagin- 

 ation. At the pole of the larva opposite the blastopore a 

 great crest of vacuolated cells — serving as a float — was 

 formed. (This crest was not seen in the larvne of the 

 first series.) The larva then assumed a triangular form, 

 the ccelom appeared at the apex of the archenteron as a 

 bilobed vesicle, and the crest slowly diminished in size. 

 The coelomic vesicle divided into right and left halves ; of 

 these, first the left, then the right, divided into anterior 

 and posterior parts. .Somewhat later, from the anterior 

 portion of the vesicle of both sides a sac was budded off; 

 that of the left side became five-lobcd, and gave rise to 

 the \vater-vasrular system ; that of the right side generally 

 remained small, but' sometimes also assumed the five-lobed 

 form, showing that it is a rudimentary fellow of the water- 

 vascular system. The larva of Ophiothrix fragilis affords 

 final and convincing proof that the echinodcrm larva 

 possesses three somites, the middle one of which becomes, 

 on the left side, the water-vascular system. 



The differences in the early phas<?s of development of 

 the two series above described are probably attributable to 

 NO. 1977, VOL. 76] 



the fact that the eggs withdrawn from the female and 

 artificially fertilised were not quite ripe, and therefore not 

 quite of the same chemical composition as those naturally 

 shed. In certain features the development of the artifici- 

 ally fertilised eggs resembles that of Ophiothrix brevis, a 

 species with shortened development, a fact which leads 

 the author to ask if mutations may not be due to slight 

 chemical differences in ova at the moment of fertilisation. 



Sex in Crustacea, and the Nature of Hermaphroditism. 



Mr. Geoffrey Smith's studies upon parasitic castration 

 show that animals belonging to widely different phyla, 

 but especially Crustacea, when attacked by various para- 

 sites, undergo an alteration in their sexual nature. At 

 first the gonad in both se.xes degenerates to a greater or 

 less extent ; thi' males assume in varying degrees the 

 secondary sexual characters proper to the female, while 

 those of the male practically disappear ; the females, with- 

 out assuming any male characters, suffer a certain amount 

 of degeneration of the secondary characters, e.g. the 

 ovigerous appendages. Finally, either on recovery from 

 the parasite or during the degenerative process, the male 

 may develop ova of large size in the testis, alongside 

 mature spermatozoa. The females never produce sperm- 

 atozoa in their ovaries. These results, which apply 

 especially to the effects of the parasitic Rhizocephala upon 

 the crabs they infect, show that hermaphroditism can be 

 called forth by an external cause acting upon a sexually 

 difforetitiated animal, and that it can only be called forth 

 in the male, not in the female. A partial temporary 

 hermaphroditism is assumed by other Crustacea (e.g. the 

 crayfish, spider-crab, and Orchestia) at particular seasons 

 when a period of growth, as opposed to one of reproduc- 

 tion, is being initiated. The conclusion that hermaphro- 

 ditism is a property of the male sex, developed in response 

 to altered conditions of metabolism, can be applied to this 

 state as found normally in Cirripedes and parasitic 

 Isopods, both of which lead a sessile, inactive existence 

 when adult, and have their vegetative functions developed 

 to a high degree. In the parasitic Isopods all the 

 individuals arc at first free-swimming males, which, on 

 settling down to their parasitic life, develop the hitherto 

 latent female part of their organisation. The presence in 

 some Cirripedes of males which may degenerate com- 

 pletely, e%'en in the larval stage, and other facts, suggest 

 tli'al all the individuals are priinarily males and subse- 

 quently females. 



Mr. F. .\. Potts confirmed Mr. Smith's results from his 

 study of the effects of Peltogaster on the hermit-crab, in 

 which also the assumption of the character of the opposite 

 sex is confined to the male. Especially interesting is the 

 appearance, in parasitised males, of the tufts of hair 

 modified for egg-bearing, and the testes in many cases 

 contain ova. 



Experiments on Seasonally Dimorphic Forms of African 

 Lepidoptera. 

 Dr. F. A. Dixey stated that it is often found that the 

 successive broods of Lepidoptera produced in the course 

 of a year differ widely in appearance according to the 

 ineteorological conditions prevailing during their immature 

 stages, the contrast being especially marked w'here there 

 is a sharp distinction between the periods of rain and dry 

 weather. Mr. Guy Marshall, working at Salisbury, in 

 Mashonaland, has succeeded in showing that, by artificially 

 varying the conditions to which the butterflies are exposed 

 during their immature stages, it is possible to bring about 

 in the midst of one season the emergence of a form 

 which under natural conditions would only have been pro- 

 duced in the other. The period during which the animal 

 is susceptible to climatic influences varies in different 

 soecies, the critical stage being in some cases confined to 

 the larval, in others to the pupal, condition. In one 

 instance (Belenois severina) the effect of moisture com- 

 bined with heat differs entirely from the effect of the 

 former alone. 



The Function of the Spiracles in Sharks and JJays. 

 Mr. A. D. Darbishire concludes that in the dog-fish 

 water is drawn into the pharynx by way of the spiracles, 

 and to some extent by the mouth, and is expelled through 



